Pacific Northwest Sitka Spruce Forest

This ecological system is restricted to the hypermaritime climatic areas near the Pacific Coast from Point Arena, California, north to northern Vancouver Island, British Columbia. These forests are typically dominated or codominated by Picea sitchensis and often have a mixture of other conifers present, such as Tsuga heterophylla, Thuja plicata, Pseudotsuga menziesii, or Callitropsis nootkatensis. Tsuga heterophylla is very often codominant. In the southern extent (in Oregon, but not in California), Abies grandis, Acer circinatum, Alnus rubra, Acer macrophyllum, Chamaecyparis lawsoniana, and Frangula purshiana can be associates, while Callitropsis nootkatensis is completely absent. Wet coastal environments that support stands of Chamaecyparis lawsoniana in the absence of Picea sitchensis are also part of this system. The understory is rich with shade-tolerant shrubs and ferns, including Gaultheria shallon, Vaccinium ovatum, Polystichum munitum, Dryopteris spp., and Blechnum spicant, as well as a high diversity of mosses and lichens. This ecological system is restricted to the hypermaritime climatic areas near the Pacific Coast from Point Arena, California, north to northern Vancouver Island and Smith Sound on the mainland coast of British Columbia. They are generally limited to areas within 25 km or so of saltwater and are most abundant along the coast of Vancouver Island, southern portions of coastal mainland British Columbia, and the Olympic Peninsula of Washington. This ecosystem is defined as the "Seasonal Rain Forest" by Wolf et al. (1995), as the climate has abundant rainfall in the winter months and very little in the summer months. At the northern boundary this Sitka spruce forest ecosystem merges into Alaskan Pacific Maritime Sitka Spruce Forest (CES204.151) which has more continuous year-round rainfall and lacks Douglas-fir. North Pacific Seasonal Sitka Spruce Forest (CES204.841) occurs on outermost coastal fringe where salt spray is prominent, riparian terraces and valley bottoms near the coast where there is major fog accumulation, and on steep, well-drained productive slopes not directly adjacent to the outer coast but within the hypermaritime zone. Annual precipitation ranges from 65 to 550 cm, with the majority falling as rain. Winter rains can be heavy. When summer drought occurs it is typically short in duration and ameliorated by frequent, dense coastal fog and cloud cover. In fact the fog belt becomes more and more important in the southern half of this ecosystem's distribution. In Washington and Oregon, it is found mostly below 300 m elevation. It also occurs as a very narrow strip or localized patches along the southern Oregon and northern California coasts. The disturbance regime is mostly small-scale windthrow or other gap mortality processes (though there are occasional widespread intense windstorms) and very few fires, the latter mainly in Oregon.

These forests are typically dominated or codominated by Picea sitchensis and often have a mixture of other conifers present, such as Tsuga heterophylla, Thuja plicata, Pseudotsuga menziesii, or Callitropsis nootkatensis (= Chamaecyparis nootkatensis). Tsuga heterophylla is very often codominant. In the southern extent (in Oregon, but not in California), Abies grandis, Acer circinatum, Alnus rubra, Acer macrophyllum, Chamaecyparis lawsoniana, and Frangula purshiana (= Rhamnus purshiana) can be associates, while Callitropsis nootkatensis is completely absent. Wet coastal environments that support stands of Chamaecyparis lawsoniana in the absence of Picea sitchensis are also part of this system. The understory is rich with shade-tolerant shrubs and ferns, including Gaultheria shallon, Vaccinium ovatum, Polystichum munitum, Dryopteris spp., and Blechnum spicant, as well as a high diversity of mosses and lichens.

From Vancouver Island south, the forest is not confined to fjords, but a marked orographic effect from the Coast and Cascade ranges limits its interior extent. At its southern extent, the zone narrows again, confined to the fog belt not by mountains but by moisture. It is restricted to the hypermaritime climatic areas (Meidinger and Pojar 1991) near the Pacific Coast, along a fog belt from Point Arena, California, north to northern Vancouver Island, British Columbia. These forests are generally restricted to areas within 25 km of saltwater and are most abundant along the coast of Vancouver Island, southern portions of coastal British Columbia, and the Olympic Peninsula of Washington. Sites include the outermost coastal fringe where salt spray is prominent, riparian terraces and valley bottoms near the coast where there is major fog accumulation, and in the northern half of its range starting in central British Columbia, steep, well-drained productive slopes not directly adjacent to the outer coast but within the hypermaritime zone (Banner et al. 1993, Green and Klinka 1994, Steen and Coupe 1997). Annual precipitation ranges from 65 to 550 cm, with the majority falling as rain. Winter rains can be heavy. The climate has more seasonal rainfall than coastal areas to the north, with a pronounced drought in summer months. Summer drought does occur, but it is typically short in duration and ameliorated by frequent, dense coastal fog and cloud cover. This forest type also dominates lower elevations (to 350 m) on the leeward side of the Queen Charlotte Islands in British Columbia. In Washington and Oregon, it is found mostly below 300 m elevation. It also occurs as a very narrow strip or localized patches along the southern Washington, Oregon and northern California coasts.

The disturbance regime is mostly small-scale windthrow or other gap mortality processes (though there are occasional widespread intense windstorms) and very few fires, the latter mainly in Oregon. Sitka spruce acts as an early colonizer of disturbed sites, such as land slumps, fluvial deposits, recently deglaciated areas. Seeds germinate best on bare mineral soil, a mixture of mineral soil and organic soil, and nurse-logs (Sawyer et al. 2009). Landfire (2007a) model: The disturbance regime is mostly small-scale windthrow or other gap mortality processes (though there are occasional widespread intense windstorms) and very few fires, the latter mainly in Oregon. Where fire does occur, it is usually stand-replacing, with a fire return interval of 300-1000 years or longer. In most of the range of the type, windthrow is a more significant catastrophic disturbance than wildfire. Windthrow "rotation" is estimated to be between 100-200 years, (but can be up to 1000 years due to patchiness). The effects of windthrow are strongly correlated with topography and adjacent land use (e.g., clearcuts). Landfire VDDT models: R#SSHE Sitka spruce - hemlock.

Conversion of this type has commonly come from logging and residential and commercial development. Many, if not all, threats to Sitka spruce forest are the same as threats to western hemlock - Douglas-fir forests, well described by the Washington Natural Heritage Program. Those stressors and threats are repeated here: Logging, development, timber harvest, road building, tree plantations and introduced diseases have all impacted natural disturbance regimes, forest structure, composition, landscape patch diversity, and tree regeneration. Development has fragmented the landscape changing fire regimes and connectivity serious affecting this small patch system particularly in lowlands. Timber harvest operations change canopy structural complexity and abundance of large woody debris of individual stands and has altered whole landscape patch pattern, age and structural complexity (Van Pelt 2007, as cited in WNHP 2011). Plantation forestry has changed local tree gene pools, horizontal arrangement of trees and homogenized the diversity of tree sizes. Other effects include loss of early-seral shrub species, advanced stand development, increased stand density, and increased tree mortality. Older logged areas can support dense, stagnating second growth with root rot (Arno 2000, as cited in WNHP 2011). Ohlman and Waddel (2002) (as cited in WNHP 2011) speculated that snag abundance more likely reflect recent disturbance and forest succession, whereas down wood amounts more are strongly reflect long-term stand history and site productivity (WNHP 2011).

Across the range of this ecosystem, there is consistent projected warming and decrease in regional precipitation patterns. In the Pacific Northwest, regionally downscaled climate models project increases in annual temperature of, on average, 3.2°F by the 2040s. Projected changes in annual precipitation are small (+1-2%), but some models project wetter autumns and winters and drier summers. Increases in extreme high precipitation (falling as rain) in the western Cascades and reductions in snowpack are key projections from high-resolution regional climate models (Littell et al. 2009). Warmer temperatures will result in more winter precipitation falling as rain rather than snow throughout much of the Pacific Northwest, particularly in mid-elevation basins where average winter temperatures are near freezing. In BC's central and north coast projections into the 2050s are 2.1 to 2.3°C annual increase that is 7-12% relative to 1961-1990 annual temperatures (Werner 2011).

In northwestern California, regional climate models project mean annual temperature increases of 1.7-1.9°C (3.06-3.42°F) by 2070 (PRBO Conservation Science 2011). And regional climate models project a decrease in mean annual rainfall of 101 to 387 mm (4-15 inches) by 2070. Currently, there is greater uncertainty about the precipitation projections than for temperature in northwestern California, but with some evidence for a slightly drier future climate relative to current conditions (PRBO Conservation Science 2011). With increased fire frequency due to warmer temperatures resulting in drier fuels, the area burned by fire regionally is projected to double by the 2040s and triple by the 2080s (Littell et al. 2009). Less rainfall and higher temperatures may shift species composition, to more drought-tolerant species, and may also which may favor non-native species. In many coastal regions, the interaction between oceanographic and terrestrial air masses may be ecologically important. Intensifying upwelling along the California coast under climate change may intensify fog development and onshore flows in summer months, leading to decreased temperatures and increased moisture flux over land (Snyder et al. 2003, Lebassi et al. 2009, as cited in PRBO Conservation Science 2011). Coastal terrestrial ecosystems could benefit from these changes. However, current trends in fog frequency along the Pacific coast from 1901-2008 have been negative (Johnstone and Dawson 2010, as cited in PRBO Conservation Science 2011), thus the effect of climate change on coastal fog remains uncertain. Summer-time fog and its associated fog-drip and cooling effect may increase with warmer inland air temperatures (PRBO Conservation Science 2011), but this will depend on oceanic circulations and he complex interaction of the El Niño-Southern Oscillation and the Pacific Decadal Oscillation makes prediction of land/ocean interaction difficult and increases the uncertainty of regional climate modeling outcomes (Karl et al. 2009). Drier overall climate may drive this ecosystem to a drier Douglas-fir-dominated type with the loss of Sitka spruce, as this species is limited to maritime climate with abundant moisture throughout the year (Harris 1990), and in the southern extent of its range, summer fog and moist maritime air are important to maintain growth (Harris 1990). However, regional climate model simulations generally predict increases in extreme high precipitation over the next half-century, particularly around Puget Sound (Spittlehouse 2008, Littell et al. 2009).

This ecological system is restricted to the hypermaritime climatic areas near the Pacific Coast from Point Arena, California, north to northern Vancouver Island and Smith Sound on the mainland coast of British Columbia (S. Saunders pers. comm. 2013), where it merges with its northern counterpart, Alaskan Pacific Maritime Sitka Spruce Forest (CES204.151).